PROJECT SUMMARY: A key challenge in combating the opioid epidemic has been connecting individuals with opioid use disorder to evidence-based treatments. The President's Commission on Combating Drug Addiction and the Opioid Crisis and others have suggested that telemedicine for substance use disorder (?tele- SUD?) may be part of the solution. In preliminary analyses, we have found that tele-SUD use is growing rapidly, and there is widespread policy interest in Congress and state legislatures in how to accelerate this growth. The SUPPORT for Patients and Communities Act, signed into law in October 2018, includes several provisions intended to reduce barriers to tele-SUD use and will likely increase the availability of and reimbursement for tele-SUD. However, despite the widespread interest and growing use, there has never been a rigorous assessment of tele-SUD. For example, what are the different tele-SUD models being used to treat opioid use disorder, what barriers exist to greater use of tele-SUD, and is tele-SUD use associated with improved (or potentially worse) quality of care for people with opioid use disorder? To fill this knowledge gap, we propose a comprehensive national evaluation of telemedicine for opioid use disorder using data through 2021 from Medicaid, Medicare, and commercial insurance as well as a series of qualitative interviews. Our Aims are to: (1) describe the different models of how tele-SUD is being incorporated into opioid use disorder care and how this is changing over time, (2) identify regional factors associated with greater tele-SUD use for opioid use disorder, (3) examine the association between tele-SUD use and quality of opioid use disorder care received and whether this varies by model, and (4) describe existing tele-SUD programs, and identify barriers and facilitators to tele-SUD adoption and sustainability. The proposed mixed-methods study will help providers interested in using tele-SUD and inform ongoing debates about regulations and reimbursement for tele-SUD in Congress and state legislatures. Our goal is to highlight policies and practices that drive greater use of tele-SUD and explore its potential role in improving access to, and quality of, care for individuals with opioid use disorder. Our research will help inform how tele- SUD may be leveraged to combat the opioid epidemic as well as other substance use disorders, such as alcohol and methamphetamine use disorders.